SPI with display modules in Raspberry Pi - Mini Project: Build & Apply

SPI Communication with a Display Module on Raspberry Pi

📖 Scenario: You have a Raspberry Pi connected to a small SPI display module. You want to send simple messages to the display using SPI communication.This project will guide you through setting up SPI communication, configuring the display, sending data, and showing the message on the display.

🎯 Goal: Build a Python program that sends a message to an SPI display module connected to your Raspberry Pi and shows the message on the screen.

📋 What You'll Learn

Use the spidev library to communicate over SPI

Create a message string to send

Send the message bytes over SPI

Print confirmation that the message was sent

💡 Why This Matters

🌍 Real World

SPI is a common way to connect small displays to microcontrollers and single-board computers like Raspberry Pi. This project shows the basics of sending data to such displays.

💼 Career

Understanding SPI communication and how to send data to hardware devices is important for embedded systems, IoT development, and hardware interfacing roles.

1

Set up SPI communication

Import the spidev module and create an SPI object called spi. Then open SPI bus 0, device 0 using spi.open(0, 0).

Raspberry Pi

import spidev

# Create SPI object and open bus 0, device 0
# Your code here

Hint

Use spidev.SpiDev() to create the SPI object and open(0, 0) to select bus 0 and device 0.

2

Configure SPI speed

Set the SPI maximum speed to 500000 (500 kHz) by assigning spi.max_speed_hz = 500000.

Raspberry Pi

import spidev

spi = spidev.SpiDev()
spi.open(0, 0)

# Set SPI max speed to 500000 Hz
# Your code here

Hint

Assign the value 500000 to spi.max_speed_hz to set the speed.

3

Send a message string over SPI

Create a variable called message with the string 'Hello SPI Display'. Then send the message bytes over SPI using spi.xfer2(list(message.encode())).

Raspberry Pi

import spidev

spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 500000

# Create message variable and send it over SPI
# Your code here

Hint

Use message.encode() to convert the string to bytes, then convert to a list for xfer2.

4

Print confirmation message

Print the text 'Message sent to SPI display.' using print().

Raspberry Pi

import spidev

spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 500000

message = 'Hello SPI Display'
spi.xfer2(list(message.encode()))

# Print confirmation message
# Your code here

Hint

Use print('Message sent to SPI display.') to show confirmation.

Practice

1. What is the main purpose of using SPI with display modules on a Raspberry Pi?

easy

A. To power the display module

B. To connect the Raspberry Pi to the internet

C. To store files on the Raspberry Pi

D. To send commands and data quickly to the display

Solution

1. Step 1: Understand SPI role

   SPI is a communication protocol used to send data between devices quickly.

2. Step 2: Connect SPI to display modules

   On Raspberry Pi, SPI sends commands and data to control display modules efficiently.

3. Final Answer:

   To send commands and data quickly to the display -> Option D

4. Quick Check:

   SPI = fast data transfer to display [OK]

Hint: SPI is for fast data transfer to devices like displays [OK]

Common Mistakes:

• Confusing SPI with internet connection
• Thinking SPI stores files
• Assuming SPI powers devices

2. Which of the following is the correct way to open SPI bus 0, device 0 using the spidev library in Python?

easy

A. spi = spidev.SpiDev(); spi.open(0, 0)

B. spi = spidev.open(1, 0)

C. spi = spidev.open(0, 0)

D. spi = spidev.SpiDev.open(0, 0)

Solution

1. Step 1: Recall spidev usage

   spidev requires creating an SpiDev object first, then calling open(bus, device).

2. Step 2: Check syntax correctness

   spi = spidev.SpiDev(); spi.open(0, 0) correctly creates spi = spidev.SpiDev() then calls spi.open(0, 0).

3. Final Answer:

   spi = spidev.SpiDev(); spi.open(0, 0) -> Option A

4. Quick Check:

   spidev object then open() method [OK]

Hint: Create SpiDev object before calling open() [OK]

Common Mistakes:

• Calling spidev.open() directly without object
• Using wrong bus or device numbers
• Using incorrect method syntax

3. What will be the output of this Python code snippet using spidev?

import spidev
spi = spidev.SpiDev()
spi.open(0, 0)
response = spi.xfer2([0xAA, 0x55])
spi.close()
print(response)

medium

A. [170, 85]

B. Depends on the connected SPI device response

C. An error because xfer2 needs a string

D. [0, 0]

Solution

1. Step 1: Understand xfer2 function

   spi.xfer2 sends bytes and returns the response bytes from the SPI device.

2. Step 2: Recognize device dependency

   The returned list depends on the connected device's response, so output varies.

3. Final Answer:

   Depends on the connected SPI device response -> Option B

4. Quick Check:

   SPI response varies by device [OK]

Hint: SPI transfer output depends on device response [OK]

Common Mistakes:

• Assuming output equals input bytes
• Thinking xfer2 requires string input
• Expecting fixed output without device

4. You wrote this code to send a command to your SPI display but it raises an AttributeError:

import spidev
spi = spidev.open(0, 0)
spi.xfer2([0x01])
spi.close()

What is the error and how to fix it?

medium

A. spidev has no open() function; create SpiDev object first

B. xfer2() requires a string, not a list

C. spi.close() should be called before xfer2()

D. Bus number 0 is invalid on Raspberry Pi

Solution

1. Step 1: Identify AttributeError cause

   spidev module does not have open() function; open() is method of SpiDev object.

2. Step 2: Correct usage of spidev

   Create spi = spidev.SpiDev() first, then call spi.open(0, 0) to fix error.

3. Final Answer:

   spidev has no open() function; create SpiDev object first -> Option A

4. Quick Check:

   Use SpiDev() object before open() [OK]

Hint: Always create SpiDev() object before open() [OK]

Common Mistakes:

• Calling spidev.open() directly
• Passing wrong data type to xfer2()
• Closing SPI before transfer

5. You want to send a command byte 0xA5 followed by data bytes [0x01, 0x02, 0x03] to an SPI display using spidev. Which code correctly sends the command first, then the data, assuming spi is already opened?

hard

A. spi.writebytes([0xA5, 0x01, 0x02, 0x03])

B. spi.xfer2([0xA5, 0x01, 0x02, 0x03])

C. spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03])

D. spi.writebytes([0xA5]); spi.writebytes([0x01, 0x02, 0x03])

Solution

1. Step 1: Understand command and data separation

   Many SPI displays require sending command and data separately to distinguish them.

2. Step 2: Check code options

   spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03]) sends command byte first, then data bytes in separate calls, matching typical display protocol.

3. Final Answer:

   spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03]) -> Option C

4. Quick Check:

   Separate command and data transfers [OK]

Hint: Send command and data in separate SPI transfers [OK]

Common Mistakes:

• Sending command and data in one transfer
• Using writebytes() which may not return response
• Not separating command from data